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Blood defence Australian researchers have uncovered two molecules in human platelets that work together to kill malaria.

The finding also provides a new explanation for why malaria is a particular problem in Africa.

In a paper published today in the journal Science, Macquarie University researcher Associate Professor Brendan McMorran and colleagues reveal platelet factor 4 (PF4) and the Duffy antigen receptors working in combination kill the malarial parasite Plasmodium falciparum.

P. falciparum is responsible for the majority of the estimated 655,000 deaths from malaria each year - mostly in sub-Saharan Africa.

In a commentary on the McMorran paper, Professor Michael Good at Griffith University and Dr Christian Engwerda, of the Queensland Institute of Medical Research, say better understanding of how the human body protects itself against malaria is needed to develop new vaccines and new therapies.

They say the role of platelets, normally thought of as being critical solely to prevent haemorrhage, in malaria resistance has been "underappreciated".

McMorran's study shows PF4 plays an important role in protecting against P. falciparum by penetrating red blood cells infected by the parasite and killing it.

However it can only do this when the Duffy antigen receptor is present.

"The Duffy antigen is a docking site that appears to allow PF4 to get to the parasite," says McMorran.

"We don't know how PF4 kills the parasite, but it kills them quite effectively."

"PF4 is known to interfere with membrane functions in other microbes like bacteria, so we think a similar mechanism may work with the malaria parasite."

Missing in Africa

The finding has implications for understanding malaria infection in Africa as the Duffy antigen receptor is absent from most African populations.

McMorran says this suggests African populations without the Duffy molecule would be more susceptible to P. falciparum-related malaria.

He says the lack of Duffy antigen in these populations suggests at some point evolutionary there was a survival advantage in being Duffy-negative.

"The parasite Plasmodium vivax can only invade cells if they express the Duffy antigen," says McMorran, adding that P.vivax is not common in Africa.

"It may be that thousands of years ago to be Duffy-negative was an advantage."

McMorran ruled out the prospect of being able to re-establish the Duffy antigen receptor back into populations.

"That's a very difficult proposition and unlikely," he says.

"What [the study] does is tells us more about how the body fights malaria and highlights another problem facing us in trying to eradicate malaria."